(a) Field of Invention
The invention relates to a machine set consisting of a water turbine and a permanently coupled generator which feeds an electric network of constant frequency via a frequency-controlled converter, wherein the speed of the machine set can be adjusted so that an optimum amount of active power is delivered with maximum efficiency.
(b) Description of the Prior Art
An arrangement of this kind is known from German Pat. No. 3 005 375. In this reference, a propeller turbine with nonadjustable rotor blades, through which water flows, is coupled to a generator. The speed of this turbo set is adjusted in a given speed range via a frequency-controlled converter. Such an arrangement makes it possible to design the generator for a nominal frequency which is lower than the network frequency. Thus, the turbo set in the reference may be operated at a frequency of less than 20 Hz at the generator terminals. Thereby, noticeably lower a-c losses occur which can be taken into account in the construction of the generator especially by an increase of the power factor. Since the power output is now controlled by presetting the turbine speed on the electrical side, the control through the mechanical adjustment of the rotor blades, previously used for this purpose, can be eliminated. However, no disclosure can be found in the patent as to how a device for setting the corresponding speed reference value required therefor is designed in practice.